Elastic solids having reversible stress-induced fluidity

ABSTRACT

Elastic solids having reversible stress-induced fluidity are prepared, e.g., by combining liquid formulations with a crystalline mixed metal hydroxide conforming substantially to the formula 
     
         Li.sub.m D.sub.d T(OH).sub.(m+2d+3+n·a) (A.sup.n).sub.a 
    
      ·xH 2  O 
     where m is amount of Li, d is amount of divalent metal D, T is a trivalent metal, A represents at least one anion or negative-valence radical of valence n and a is the amount of A, and xH 2  O represents excess waters of hydration, if any. These make useful coatings. 
     The instantly reversible fluidization of these unique elastic solids may be expressed as: 
     σ=k.sub.α ε when ε&lt;F, for the solid phase; and 
     σ=f(dε&#39;/dt) when ε&#39;&gt;F, (this equation represents a generalized form for the usual theological equations); for a cycle of ε, -xF &lt;ε&lt;xF, and when ε&#39; equals 0 the liquid phase changes back to the solid phase, and 
     where the symbol σ represents stress; k.sub.α  represents an elastic spring constant for the solid phase, ε and ε&#39; are strain and F is critical strain.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of Ser. No. 07/775,662, filed Oct. 11, 1991, nowU.S. Pat. No. 5.443,761 which is a continuation-in-part application ofapplication Ser. No. 07/698,428, filed May 10, 1991, now U.S. Pat. No.5,196,143, and of Ser. No. 07/686,098 filed Apr. 16, 1991 U.S. Pat. No.5,232,627 and of continuation-in-part of application of Ser. No.07/526,970 filed May 16, 1990, now U.S. Pat. No. 5,094,778, which is acontinuing application under 37 CFR 1.62 of Ser. No. 07/282,445 filedDec. 9, 1988 (now abandoned) which is a continuing application of Ser.No. 07/047,800 filed May 7, 1987, now U.S. Pat. No. 4,790,954, which isa continuing application of Ser. No. 06/752,326 filed Jul. 5, 1985, nowU.S. Pat. No. 4,664,843. All of these are incorporated by referenceherein in their entirety.

This is also a continuation-in-part of application Ser. No. 577,825filed Sept. 4, 1990, now U.S. Pat. No. 5,154,932, which is acontinuation of Ser. No. 252,281 filed Sept. 30, 1988, which itself is acontinuation-in-part of Ser. No. 060,133 filed Jun. 9, 1987 (now U.S.Pat. No. 4,990,268), which is a continuation of Ser. No. 752,325 filedJul. 5, 1985 (now abandoned). The above parent application Ser. No.577,825 filed Sep. 4, 1990 is also a continuation-in-part of applicationSer. No. 07/698,428, filed May 10, 1991, now U.S. Pat. No. 5,196,143,and of Ser. No. 07/686,098 filed Apr. 16, 1991 and ofcontinuation-in-part of pending application Ser. No. 07/526,970 filedMay 16, 1990, which is a continuing application under 37 CFR 1.62 ofSer. No. 07/282,445 filed Dec. 9, 1988 (now abandoned) which is acontinuing application of Ser. No. 07/047,800 filed May 7, 1987, nowU.S. Pat. No. 4,790,954, which is a continuing application of Ser. No.06/752,326 filed Jul. 5, 1985, now U.S. Pat. No. 4,664,843. All of theseare incorporated by reference herein in their entirety.

This is also a continuation-in-part of abandoned application Ser. No.07/609,966 filed Nov.6, 1990 which itself is related to above said Ser.No. 060,133 filed Jun. 9, 1987 (now U.S. Pat. No. 4,990,268), which is acontinuation of Ser. No. 752,325 filed Jul. 5, 1985 (now abandoned).

Other patents containing related subject matter are U.S. Pat. No.4,822,421; U.S. Pat. No. 4,999,025; and U.S. Pat. No. 5,015,409, thislatter patent being a continuation-in-part of above said Ser. No.060,133 filed Jun. 9, 1987 (now U. S. Pat. No. 4,990,268), which is acontinuation of Ser. No. 752,325 filed Jul. 5, 1985 now abandoned.

FIELD OF THE INVENTION:

Elastic solids which undergo a reversible phase change to a fluid stateunder stress, but which immediately revert to their elastic solid statephase when at rest.

BACKGROUND OF THE INVENTION

It has been disclosed in the above-identified applications and patentsthat certain crystalline layered mixed metal hydroxides and activatedmixed metal hydroxides can be used in the modification of the viscosityof various fluid formulations. In some of the disclosures, the saidmixed metal hydroxides are combined with clay, e.g. bentonite andothers, and with fine-particle silica, to form adducts which are usefulfor viscosity modification of drilling fluids and other fluids. In somecases, the viscosity is said to be thixotropic, and in other cases theviscosity is merely said to be thickened or modified. Also, some of theabove-identified pending applications disclose that fluids gelled by useof the crystalline layered mixed metal hydroxides will quickly re-gelafter being subjected to shear.

In a paper prepared for presentation at the 1990 Drilling Conference ofthe International Association of Drilling Contractors/Society ofPetroleum Engineers in Houston, Tex., Feb. 27-Mar. 2, 1990, the efficacyof using MMH (Mixed Metal Hydroxides) in a drilling mud are disclosed.The paper, in its References section on page 5, refers to other papersabout the use of MMH in drilling muds at meetings of the IAPC/SPE andSPE Symposium on Oilfield Chemistry in February-March 1989. Thesepublications are cumulative to the information disclosed in U.S. Pat.Nos. 4,664,843 and 4,790,954, the publication of which predates thesepapers.

None of the patents identified above disclose any recognition of anentirely novel type of viscosity effect which is not of the formspreviously known, i.e, those known to rheologists as dilatant,thixotropic, Newtonian, non-Newtonian, psuedo-plastic, Bingham plastic,or rheopexic.

We have now discovered more about some of these reported compounds andformulations containing them and have discovered some which undergo aphase change from an elastic solid state to a fluid state under theforce of stress, rather than shear, and which immediately revert to anelastic solid state upon cessation of the stress; this is an unexpectedphenomenon- which we believe has not been previously recognized orreported by others, and is believed to be unique. In a manner ofspeaking, it is a phase metamorphosis, not a chemical metamorphosis.

The phase change of going from an elastic solid phase to a fluid phaseby the applying a fluidizing amount of stress, and then reversion backto the elastic solid phase upon cessation of the stress, is notperceived as a viscosity modification in the ordinary sense of the term"viscosity modification".

For example, changing of a Newtonian liquid to a non-Newtonian liquid,or vice-versa, is one form of a viscosity modification. Changing thedegree or extent of thixotropicity or dilatancy of a liquid is a form ofviscosity modification. These viscosity modifications are not perceivedas being a phase change from an elastic solid phase to a fluid phase.

Instead, our new discovery is perceived as a reversible phase change ofan elastic solid composition having high energy, short range ionicinteractions with a very low degree of reinforcement. Because of this astress-induced fluidization of the elastic solid is reversible, sincethe high energy, short range interactions are not destroyed, and the lowdegree of reinforcement permits the fluidization until reversion back toan elastic solid.

These elastic solids having reversible stress-induced fluidity areperceived as being analagous, in their response to a critical stress, toa solid-state diode in response to a flow of electrons and the cessationof the flow of electrons.

This novel phase change effect is herein given the name of"stress-dependent fluidity" as a means of identifying the effect on anelastic solid which instantly becomes a relatively low-viscosity fluidunder a critical stress. The change from an elastic solid phase to afluid phase begins as soon as the critical stress is applied and thereversion to an elastic solid phase is immediate upon ceasing thestress; by "immediate" it is meant that the reversion to the elasticsolid state is a fraction of a second, essentially too fast for visualperception or for measurement using state of the art measuring devices.It is not the same effect as is obtained using shearing forces to breakup a gel or a sol since those do not immediately return to the form of agel or sol, (such as hydrogel, alcogel, organogel, or electrosol) thoughmany will return, at least to some degree, to a gel or sol over adetectable period of time. Some of the various previously known forms ofgels or sols may even undergo changes under shearing forces whichinterfere with, or even prevent a complete return to their previous formupon cessation of the shearing forces.

SUMMARY OF THE INVENTION

It has now been found that novel elastic solids having stress-inducedfluidity are prepared by creating a fluid having distributed thereinionic charge sites and also having distributed therein counter-ioniccharge sites, the charge sites being present in the fluid in sufficientquantity to produce an elastic solid having stress-induced fluidity.Preferably, the ionic charge sites are anionic, the counter-ionic chargesites are cationic, and the chemical moieties containing the ionic sitescomprise about 0.1 to about 50 percent of the total weight of theelastic solid. When stress is applied to the elastic solid, the elasticsolid is strained until it suddenly becomes fluidized. The point atwhich fluidization occurs is referred to here as the criticalstress/strain relationship, which is computed as the critical strainpoint.

The instantly reversible fluidization of these unique elastic solids maybe expressed as:

σ=k.sub.σ ε when ε<F, for the solid phase; and

σ=f(dε'/dt) when ε'>F, (this equation represents a generalized form forthe usual theological equations); for a cycle of ε, -xF <ε<xF, and whenε'equals 0 the liquid phase changes back to the solid phase, and

where the symbol σ represents stress; k.sub.α represents an elasticspring constant for the solid phase, ε and ε' are strain and F iscritical strain.

Compositions comprising elastic solids having stress-dependent fluidityare found to be useful in a variety of applications for obtaining usefuleffects of the unique properties of the compositions. Such compositionswhich benefit from the properties include a variety of coatings,adhesives, gels, resins, and fluids. The fluids comprise aqueous andorganic fluids, such as paints, sealers, fillers, glues, protectivecoatings, temporary coatings, and the like. The fluids can be latex,dispersions, emulsions, solutions, acrylics, acrylates, resins, epoxies,urethanes, rubbers, polyolefins, polyglycols, polyesters,polycarbonates, condensation polymers, polyethers, and the like.Temporary coatings, such as de-icing formulations for airplane wingsawaiting take-off, can be formulated as elastic solids which can beblown off the wings by the total stress placed on the formulation by aircurrents during flight.

Notable among the compounds which are used in preparing these elasticsolids, by being added to the desired fluid, are crystalline layeredmixed metal hydroxides, including those prepared in aqueous systems,those prepared in non-aqueous systems, and those prepared in acombination of aqueous/non-aqueous systems. Also, adducts of the mixedmetal hydroxides are found to be useful in preparing the elastic solidshaving stress-dependent fluidity by being added to the desired fluid.Preferably the mixed metal hydroxides include aluminum as one of themetals, along with a divalent metal, especially magnesium, and, in somecases, including a monovalent metal, especially lithium. Furthermore,the crystalline layered mixed metal hydroxides may, at times, be calledmixed metal oxyhydroxides or mixed metal hydrous oxides. The expressionrefers to a crystalline structure which contains at least two metals,not to a mere mixture of metal compounds. Most preferable are thecrystalline mixed metal hydroxides, crystalline mixed metal oxides, andcrystalline mixed metal oxy-hydroxides of Mg and Al One can begin withanhydrous forms, if desired, and high-temperature activated forms of themixed metal compounds can be used.

We have found that there are many compositions or formulations whichbecome elastic solids exhibiting stress-dependent fluidity when combinedwith an effective amount of at least one of the crystalline, layeredmixed metal compounds disclosed herein. There are so many permutationsof combinations of the mixed metal compounds and the fluids to whichthey are 'added to achieve stress-dependent fluidity, that absolutenumerical ranges are difficult to define. The amount of a given mixedmetal compound of this present invention needed to produce an elasticsolid having stress-dependent fluidity can be easily determined bytesting a few concentrations, usually less than about 10% by weight ofthe mixed metal compound in the total weight of the combinedingredients. A person skilled in these relevant arts of adjusting theproperties of a fluid, and being informed of the present invention, willrecognize when a formulation has taken on the appearance of an elasticsolid which undergoes a phase change to a low viscosity fluid under theinfluence of stress and which immediately reverts to the elastic solidphase upon cessation of the fluidizing stress.

DETAILED DESCRIPTIONS INCLUDING BEST MODE KNOWN

As used herein, the term "stress-dependent fluidity" refers to thefluidization of an elastic solid, which is in contact with a substrate,upon application of a force which induces the elastic solid to undergo aphase change to a fluid state, rather than plastic deformation, and flowalong, or upon the substrate. It immediately recovers its elastic solidstate upon cessation of the stress, though the shape and/or position onthe substrate has been been changed. Considering that a new concept ofobtaining stress-dependent liquid flow phase in an elastic solid isencountered here as a reversible phase change, then appropriate means ofdescribing this unique phenomenon are attempted here.

The term "plug flow" is used in the customary manner to indicate thatflow is not turbulent flow, but is substantially uniform and monolithicalong a flow path, even though there may be some laminar flow due tofriction along the interface of the substrate on which there is flow andwhich tends to hold back ("drag") the fluid.

As used herein, the term "activated" (a term often used in the field ofminerals and inorganic chemistry) refers to the heating (thermalactivation) of metal hydroxides or hydrous metal oxides, sometimes inthe presence of CO₂, to a temperature high enough to drive off thewaters of hydration, leaving the metals as "active" metal oxides oroxy-hydroxides. Activation of hydrous mixed metal oxides and the like isillustrated in pending application Ser. No. 686,098 filed Apr. 16, 1991and now U.S. Pat. No. 5,252,627 (attorney docket #C-34297-D) which isincorporated herein by reference as shown hereinbefore. The activatedMMOH (hereinafter sometimes referred to as an AHMMO) and other AHMMOcompounds, which are arid, are very friable (easily decrepitated), andeasily disperse in water as very small crystals, generally of colloidalsize. While one may encounter a chemical method for creating activatedmetal oxides or oxy-hydroxides, the thermal method would be expected tobe the easiest and least expensive method.

In one aspect the present invention embodies the making of clay adductswith activated MMOH of the monolayer and the multi-layer variety as wellas natural and synthetic hydrotalcites (expressed here simply as MgO·Al₂O₃ or MgAl₂ O₄ since those are the principal components) and other formsof activated mixed metal oxides or mixed metal oxy-hydroxides includingAHMMO.

For example, hydrotalcite is a naturally occurring mineral (thatcontains some CO₂ in its structure) which, when thermally dehydrated,yields an active magnesium aluminum oxide compound or oxyhydroxidecompound. Also for example, magnesium hydroxide and aluminum hydroxidecan be combined (especially in the presence of some CO₂) and heated toyield mixed metal oxides conforming essentially to the formula(MgO)x·Al₂ O₃, where the ratio of Mg/Al can vary over the range of about0.01/1 to about 6/1, preferably about 0.5/1 to 4/1. Below that range theamount of MgO may not be sufficient to yield a mixed metal oxide whichbehaves efficiently in the present invention. Above about 4/1, theamount of excess MgO is likely to form a single metal oxide which ispresent with the mixed metal oxide structure, but as a separate phase.

U.S. Pat. No. 4,748,139 discloses the thermal activation of mixed metalhydroxides at about 500° C. These activated mixed metal oxides were thenmade into dense spinel structures at above 1000° C. Examples are shownstarting with Mg(OH)₂ mixed with NaAlO₂ and digested at 10506 to form alayered magnesium hydroxide/aluminum hydroxide which forms MgAl₂ O₄ whenheated above 500° C. While this patent teaches the making of someactivated mixed metal oxides, it does not each the formation of anadduct of clay with the activated mixed metal oxides. Neither does itdisclose the making of an elastic solid which can undergo a reversiblephase change and be caused to flow by the force of stress and recoverits elastic solid state upon cessation of stress.

Other than the AHMMO compounds, the MMOH compounds may be prepared inaccordance with the procedures in parent applications and progeny ofthis application listed on pages 1 and 2, especially U.S. Pat. No.4,990,268 (docket #C-33596-A) where they are prepared in aqueous mediaand Ser. No. 609,966 filed Jan. 16, 1990 and now U.S. Pat. No. 5,084,209(docket #C-37049) where are made in a non-aqueous media so as to besubsequently free of excess waters of hydration.

Natural clays and refined natural clays may vary from one mininglocation to another and the performance obtained with one batch may notexactly match the performance of another batch; the color may not matchand the effect on viscosity may not match. The natural clays, and evenrefined natural clays, may contain impurities which can producenon-uniformity among batches and may create side-reactions with otheringredients in a formulation to which the clay is added. Clays arenormally anionic and can react with ingredients which are cationic, suchas cationic surfactants used in hair conditioners or in cleansers andthe like.

We have found that activated mono-layered and multi-layered mixed metalhydroxides (MMOH) and other activated hydrous mixed metal oxides, all ofwhich are referred to here as "AHMMO", especially those which are oflayered crystalline structures exhibiting cationic surface charges, arebeneficially employed as adducts with clay and with other compounds ormaterials which are anionic.

For purposes of conciseness, the expression "MMOH" will be used in thisdisclosure to refer to the crystalline mixed metal hydroxides which aredescribed in detail below and the expression "AHMMO " will be used inreference to activated forms of the MMOH and activated forms of otherhydrous metal oxides. The AHMMO compounds which are made fromsynthetically, produced mixed metal compounds can be of substantiallyconsistent quality and purity. AHMMO compounds made fromnaturally-occurring minerals, especially hydrotalcites, which cancontain small or trace amounts of metal impurities besides the Mg and Alcomponents, are particularly useful in the present invention.

The crystalline mixed metal hydroxides (MMOH) used in the presentinvention, to create activated mixed metal oxides or oxy-hydroxides,AHMMO, conform substantially to the empirical formula

    Li.sub.m D.sub.d T(OH).sub.(m+2d+3+n·a) (A.sup.n).sub.a ·xH.sub.2 O

where m is an amount of Li of from zero to one,

where D represents at least one divalent metal cation and d is an amountof from about zero to about 4,

where T represents at least one trivalent metal cation,

where A represents at least one monovalent or polyvalent anion ornegative-valence radical,

a is an amount of A ions of valence n, with n·a being an amount of fromabout zero to about -3,

where (m+2d+3+n·a) is equal to or more than 3,

where (m+d) is not zero,

and where xH₂ O represents excess waters of hydration, with x being zeroor more.

In the above generic empirical formula, "excess waters of hydration"means that there is more water associated with the compound than isneeded to supply the amount of hydroxyl ions in the crystal structure.When there is no excess water and x is essentially zero, the compounds,AHMMO, are very fine "activated" crystals having a cationic charge whichare found to have a high affinity for forming adducts with anioniccompositions such as clay when dispersed in an aqueous liquid.

In the above formula, it should be noted that n, being the valence ofthe anion, is a negative number; thus n·a is a negative number.

The AHMMO compounds are found to be beneficial as thickeners orviscosity-modifiers for aqueous-based functional products, such ascleansers, commercial products, household products, and personal careproducts when incorporated therein, as well as forming useful adductswith clay.

In one aspect, the present invention is perceived as being a formulationof the type described having incorporated therein the MMOH or AHMMOcompounds.

In another aspect, the present invention is perceived as a means,method, or process for providing viscosity-modifiers or thickeners tothe described formulations by incorporating therein the MMOH or AHMMOcompounds, especially as adducts with clay.

A further aspect is that AHMMO compounds provide a thickened, elasticsolid product which flows readily under even slight stress, but whichrethickens rapidly to an elastic solid state when the stress is ceased.The re-thickening or gelling rate is perceived as being immediate.Liquid dispersions of clay adducts prepared in accordance with thepresent invention exhibit the novel and unique behavior of exhibitingfluidity which is stress dependent. That is, the liquid dispersion isessentially of a gelled consistency in the absence of any stress placedon it, but becomes quite fluid upon application of a stress. It exhibitsneither Newtonian activity, nor thixotropic activity, nor dilatantactivity, but instead it responds to a stress placed upon it byinstantly becoming very fluid, then when the stress is removed itreturns to its previous gelled consistency, which we refer to as anelastic solid.

Though there are many forms of clays, the clays preferred for use in thepresent adducts comprise the smectite clays, especially thebentonite-type, and montmorillonite clays. Even though this disclosureis based largely on the bentonite forms of clay, other forms and classesof clay are within the ambit of this invention, such as amorphous clay(e.g. of the allophane group) and crystalline clay (e.g. 2-layer,3-layer expanding-type, non-expanding type, elongate-type, regular mixedlayer type, and chain structure type). For example, a non-exhaustivelisting of the clays is as follows:

    ______________________________________                                        bentonite     vermiculite  kaolinite                                          chlorite      halloysite   attapulgite                                        smectite      sepiolite    montmorillonite                                    polygorskite  illite       Fuller's earth                                     saconite      and the like                                                    ______________________________________                                    

The activated MMOH and AHMMO compounds useful in the present inventionare preferably those of the monodispersed, monolayer variety such asdescribed in parent parents U.S. Pat. Nos. 4,664,843 and 4,990,268identified above. Compounds which are not of the monolayer varieties,but are of the multi-layer varieties, are shown, e.g., in U.S. Pat. Nos4,326,961; 4,333,846; 4,347,327; 4,348,295; 4,392,979; 4,446,201;4,461,714; and 4,477,367. These multi-layered varieties in the activatedform can be used in the present invention.

The process, in general, for making the multilayered varieties of mixedmetal hydroxides involves starting with a soluble compound of atrivalent metal and then reacting that with the desired solublemonovalent metal(s) and/or divalent metal(s) and converting the saidcompounds with a source of OH--ions, e.g., NH₄ OH, at a temperaturesufficient to create the multi-layered (generally 2-layer or 3-layer)crystalline mixed metal hydroxide. In contradistinction thereto, thecrystalline monolayer mixed metal hydroxides are prepared by combiningthe desired metal compounds in solution in the desired ratio and thenreacting the combination of metal compounds with a source of OH--ions atan appropriate temperature for producing the mixed metal hydroxidecrystals.

Thus, for the most part, the MMOH compounds are prepared by the generalprocess of forming a solution of compounds of the desired metals underappropriate conditions whereby a source of hydroxyl ions, e.g. ammoniumhydroxide or caustic, reacts with the soluble metal compounds to producethe layered crystals of mixed metal hydroxides. In some instances, it isoften best to avoid having residual ammonia in the product, in whichcase another hydroxy material, especially NaOH or KOH is used.

The process of using activated MMOH and AHMMO compounds to thickenaqueous-based functional products can be achieved in at least twogeneral ways. One method, in general. involves the activation of theMMOH and AHMMO particles by an electrolyte. In this process, the MMOHand AHMMO is first dispersed by using high shear, sonic waves or othermethods known in the art to produce a high degree of dispersion ofagglomerated particles. Once the material is dispersed in aqueous orpartially aqueous media, a salt (electrolyte) is added eitherpredissolved or dry and mixing/or shearing is continued until a smooth,thickened system is obtained Other ingredients may be blended into theprethickened material. Often, one or more of the ingredients is a saltand a separate activator is not needed. The salt used for activation canbe almost any ionic substance but components containing organic anionsor multivalent anions such as 603-2, P04-3, P3010-5 and the like areusually more effective.

The other general method involves interaction with other colloidalparticles in such a manner that they are linked together through bridgesor bonds formed by the MMOH and AHMMO. In these cases, it can beinterpreted as forming an adduct with the other particles. This canproduce an "extension" effect. This can happen, for instance, when fumedsilica or a clay is also an ingredient and less material is needed forthickening. This can also occur when a normally soluble material isincluded in the formulation beyond the point of saturation such thatvery small or colloidal particles are present as crystals oragglomerates. In this case, the thickening occurs when the MMOH or AHMMOand other particles are sheared together and agglomerates are broken,exposing fresh faces which react. Adducts of MMOH and fumed silica, avery fine particle form of silica, are disclosed in pending Ser. No.577,405 filed Sep. 4, 1990 and now abandoned (docket C-36361) which isincorporated herein by reference.

The expression "mixed metal hydroxide" implies that there are at leasttwo different metals in the hydrous oxide crystals. In the presentinvention, it is preferred that at least one of the metals is atrivalent metal, along with at least one other metal which can beeither, or both, of the divalent or monovalent (Li) varieties,preferably the divalent variety. The amount of the A anion (ornegative-valence radical) is that which, with the OH˜ions, substantiallysatisfies the valence requirements of the cations in the crystallinematerial.

In the above described formula, the trivalent metal cation is preferablyAl, Fe, or Ga, and can be mixtures of any of these; Al is most preferredas the trivalent metal.

The divalent metal cation is preferably Mg, Ca, Mn, Fe, Co, Ni, Cu, orZn and can be mixtures of any of these; Ca or Mg, especially Mg, is mostpreferred as the divalent metal.

The contents of the numerous formulations that can be thickened ormodified by the addition of AHMMO compounds can be varied widely.Generally, the ingredients and levels of the ingredients which are in agiven formulation have more to do with a desired effect other than thatof thickening or viscosity-modification. The versatility of the AHMMOcompounds is beneficial in that it can be added to so many formulationsfor viscosity purposes without interfering with the other ingredients intheir intended purpose. Substitutions, replacements, and/or eliminationsof one or more of the components (other than the AHMMO compound) oftenhas little effect on thickening or viscosity-modification.

In the following examples the expression "MMOH" is in reference tocertain compounds within the generic formula shown above and whichconform substantially to the formula MgAl(OH)_(5-y) Cl_(y) ·xH₂ O andwhich are prepared from an aqueous solution containing MgCl₂ and AlCl₃as taught, e.g., in U.S. Pat. No. 4,664,843 and U.S. Pat. No. 4,990,268. The small amount of Cl⁻ anion is a residual amount of the Cl⁻ anionwhich was in the starting materials.

The following examples are for illustration only, but the invention isnot limited to the particular illustrations shown.

EXAMPLE 1

One part by weight of methanol containing 2% MMOH by weight is blendedwith a polyethylene oxide compound. Methanol is then distilled out ofthe mixture and resultant product is agitated with an ultrasonic probe.The so-formed composition is an elastic solid which undergoes a phasechange by becoming fluidized instantly upon the application of a stressand which reverts to its elastic solid phase instantly upon cessation ofthe stress.

Thus the composition is readily applied onto a substrate as a fluidphase under the application of stress and remains there as an elasticsolid coating on the substrate instantly after the applicating force isstopped.

EXAMPLE 2

In accordance with Example 1 above, an epoxy resin DER 331 (Trademark ofThe Dow Chemical Company) is substituted, in like amount, for thepolyethylene oxide compound. The so-formed composition, as in Example 1,is found to undergo an instant phase change from an elastic solid phaseto a fluid phase by application of a stress force, and it reverts backto its elastic solid phase instantly upon cessation of the stress force.

The epoxy resin, being one which is curable over a very perceivable, butfinite period of time, is easily mixed with the curing agent to completethe formulation as an elastic solid, and then applied to a substrate asa fluidized composition which instantly reverts back to the elasticsolid phase upon cessation of the stress force used in applying it tothe substrate and then undergoes curing.

What is claimed is:
 1. A process comprising incorporating insubterranean operations a water-based elastic solid compositionexhibiting stress-dependent fluidity, comprisinga fluid containing anamount, sufficient to cause the fluid to be an elastic solid exhibitingstress-dependent fluidity, of a crystalline mixed metal hydroxideconforming essentially to the empirical formula

    Li.sub.m D.sub.d T(OH).sub.(m+2d+3+na) (A.sup.n).sub.a ·xH.sub.2 O

where m is an amount, in the range of zero to about 1, of Li cations, Drepresents divalent metal cations, d is an amount of D and is in therange of zero to about 4, T represents a unit amount of trivalent metalcations, A represents monovalent or polyvalent anions or negative-valentradicals of valence -n, with a being the amount of A anions; m+d isgreater than zero and (m+2d+3+na) is equal to or greater than 3, and xis zero or more if there are excess waters of hydration, said mixedmetal hydroxide being essentially uniformly distributed in the fluidsystem in an amount which produces a gel which has the characteristicsof an elastic solid having stress-dependent fluidity.
 2. The process ofclaim 1 wherein the value of m is in the range of about zero to about 1,the value of d is in the range of about 0.5 to about 2, and the amountof A is in the range of zero to about
 2. 3. The process of claim 1wherein the mixed metal hydroxide comprises monolayered, monodispersedcrystals.
 4. The process of claim 1 wherein the mixed metal hydroxidecomprises

    Mg.sub.d Al(OH).sub.(d+3+na) (A.sup.n).sub.a ·xH.sub.2 O,

where d is an amount in the range of about 0.5 to about 2, n·a is anegative amount in the range of about zero to about 1, and x is anamount of from zero to about
 6. 5. The process of claim 1 wherein thelayered hydroxide containing fluid is used in subterranean operations asa drilling fluid, drilling mud, fracture fluid, packer fluid orcompletion fluid.
 6. The process of claim 1 wherein the divalent ion ismagnesium and the trivalent ion is aluminum.
 7. The process of claim 6including using the layered hydroxide containing fluid in subterraneanoperations as a drilling fluid, drilling mud, fracture fluid, packerfluid or completion fluid.
 8. The process of claim 6 including using thelayered hydroxide containing fluid as a drilling fluid.
 9. The processof claim 1 wherein the trivalent metal cation is selected from at leastone member of the group consisting of Al, Fe and Ga.
 10. The process ofclaim 9 wherein the divalent metal cation is selected from at least onemember of the group consisting of Mg, Ca, Mn, Fe, Co, Ni, Cu and Zn. 11.The process of claim 10 including using the layered hydroxide containingfluid in subterranean operations as a drilling fluid, drilling mud,fracture fluid, packer fluid or completion fluid.
 12. The process ofclaim 1 wherein the divalent metal cation is selected from at least onemember of the group consisting of Mg, Ca, Mn, Fe, Co, Ni, Cu and Zn.